Signaling system



pril 25, 1950 J. A. RANKIN ET AL 2,505,574

SIGNALING SYSTEM Filed Aug. 2, 1943 2 Sheets-Sheet 1 TRNSM/ T TEK n un' .4 TTORNEY April 25, 1950 .1. A. RANKIN ET AL 2,505,574

` SIGNALING SYSTEM F'ilvled Aug. 2, 1945 2 Sheets-Sheet 2 l SELECTOR IN VEN TORS .HAR/.40N 0541. .Jo/1N ,4. RANK/N s.

ATTORNEY Patented Apr. 25, 1950 STATES: PATE Nr" orsi-CE 21,505,574'. v SIGNALINQ SYSTEM.v Johnw Argus CR'ankin; Chicago, Illl, William Rufuse Alexander,v Upper Montclair, N. J and Harmon.

Btncal, Bloomington, indi, assignors to;y Radio1. GorporationiofxAmerica, acorporation -of Deia-- Ware Application August'z, 1943, vSerial No. 497,000

12.0laimst. l

object# off this inventicanfr is the improved controlfrom a remote point-onaselected one of av largenumberoffope'rations.

- We attain this object-by-afnewand improvedmethodof 'andmea-nsi for generating at the control-fpoint'-orf points '-wave `energy-in which afpluf ral-ity-ofseries vofdistinctland separate incidents such as changes 'in timing a-re causedto-r` occur'. Theffrequency' of fthe generated f Wave energy on*- which the*series-iofincidents occuris changeable andthus alarge number ofi-incident combinationsv are available:r 'If-he-Lincident-c combinations may be-usedlataf-receivingpointor points to per-v form aselected --function,f' sor that an` operator at the transmitter by controlling the transmitted Wave may select and control one of a large number `of operations at a selected receiver of alarge number of separated receivers or selectedv re ceivers of groups ofreceivera or any lselected one` of alargenumber of receivers performing a single operationmayfbe controlled.

In a particularapplication i. a selected subcarrier (referredto as the intermediate. frequency at the receiver) of whichtherefare five,- is .y modulated .bya selectedffrequency; of which there areeight;y and. used tofmodulatefa selected. carrier. of which-.there .areiveigto :provide-.- 200 different combinations; TheseV transmitted combinations:` then cooperatewithV receiver." relays.. wherein-,1 10,000 diierent combinations arezprovidedsothat some .two million combinations arepossib1e.vvithnl the elements provided,v Thusrfeach of;two.million. separate -receivers .could beoperated, separately.- on its own particular. individual preset combi-- nation.. Il :several receivers. were preset. to be:A operable on the same combination. then of course, several million. receivers.. could. be remotely,.- operated.

The general idea...is thatza few orafewfhgundred:

receivers. equippedwth 'detonating mechanisms 40 may be ,remotely fired separately, .or in groups-1de-v pendingon the codingv of the ringzcombination) The high order.. of t numbers of combinations,r`

provided is to minimizethe lchanceof inadvertent..

operation of a particular'receiver. from.. noise, ..4

interference or even operation of the transmitterV to detonate mines in another area. or category- (for example, docks, airelds,v power stations or barracks .may be operated selectively). Thus,. if!

'1 or-.nearzala'nd mine-and thef-relaysitherein con1'=-A "detonating-"the associated'iland ber," of 'combinations fmay'fbef increased'E or f de.;L

creased by minor changes infthefreceiver-units.

An :additionalobj e'ctisz to Iprovidefa' system; as disclosed fb'ri'eflyabovfwhicir issecret toi a' high" degree;- This isiaccomplisli'ed by"`using1 af: fre

quency modulation of the #sub-carrier# by the-"conci` 135'? trol'throufgli afzreceiverfisfpractical-1571 nil.

i ceivers evenfbychance Vt-'explode la' minef and.a.frequencyfmodulatiomofrohezcarrierziby the frequency modulated. sub=carrier;l and byl' pro. V

lations. Moreover-r. since thetone'fselected is :rati

the; discretion-ni ofi' ther-'transmitter operator astguided by selection,(preknowledge) of the. ree*- ceiveritofbertheacontrol.'mediumfyias is the-'subfl carrier`A and* carrier f frequencyfiselected; the pos; sibility' thatairenemy transmitter :will be. operated; even 'by chance in* the; proper mann'ert7 take con# More= over; by providingf'receivers"which 4function only' on"receiptfof ther-particular "typef of modulation y we transmit; there:A is fstill"l less chance that an enemy-transmittericould- `operatethrou'g'hthe re' The? receiver fisffreef from radiation; spurious operation `A b'y eitlerfthe'- enemy erstatic; and from blocking bythe enemy.

vantages which ilow from the attainment'foffsuch obj lects lappear in"'th`ei detailed Y"description `Vwhich follows."

Inl the present application We disclosev and claimv millions of elementsmust enter into. a properwthe transmitter:

combination to securea detonation of ,a particular receiver or groupofreceivers, the..chances of inadvertentV or enemyv operation become ,vanishingly small.

IrrSeeley'U."v S. application No. 50S-,2321 iiled November 6, 1943, which ripenedinto Patent #22128,29T0n5' 'September 30;"1947; the "systemg is disclosedjwhilfe i'n'Dal; etalf; U S application on December 31, 1946 into Patent #2,413,296, the receiver is disclosed.

In describing our invention in detail reference will be made to the attached drawings, wherein Fig. 1 (sheets 1 and 2) illustrates one embodiment of our invention, while Fig. 2 illustrates in simplied form the phase shifting network used in the reactance tube modulators f the embodiment illustrated in Fig. 1.

In the gure the circuit designated Iii is a low frequency oscillation generator of the resistance capacity type arranged with switching means to generate oscillations at a plurality of diierent frequencies, in the arrangement developed, eight frequencies falling between 200 and 1200 cycles per second.

I6 is an intermediate frequency oscillator the reactance of which is adjustable by a section of the I. F. selector switch referred to more in detail hereinafter to generate sub-carriers of a selected one of ve diiferent intermediate frequencies. I6 designates generally also the reactance tube modulator including differential reactance tubes controlled by the output of the transformer in the apparatus of I4.

I2 is an attenuator network wherein is adjusted, by switching means, the amplitude of the generated tone oscillations necessary to modulate or sweep the intermediate frequency, generated at I6, through the desired range. Note that this attenuator switch is designated the I. F. selector and it comprises two ganged switch sections the other section of which is in the intermediate frequency oscillatorv I6. The ganged switch in I6 provides a means of selecting one of ve available intermediate frequencies. The ganged companion switch in I2 provides a level or gain control means toprovider the correct amplitude of audio frequencyto properly drive the two I. F. modulator tubes.

I4 represents a manual dial through which the output of IB as regulated byl I2 is fed to the transformer at 'I4 to supply the selected tone, dialed manually as desired, to I6.

I8 designates generally a resistance network by means of which the input (which is the frequency modulated output of the I. F. generator) to the second reactance tube modulator associated with the carrier generator designated generally at 2n is adiusted. Note that this input intensity adiustment switch is ganged with the switch which selects the condenser to be included in the oscillation generator frequency controlling circuit of the apparatus in 20, so that for each carrier frequency a particular input intensity is used to provide an equal sweep of the carrier throughout the range of operation. The primary v function of the gang switch in I 8-26 is to provide frequency selection-the ganged attenuator I8 merely and incidentally insures proper operating levels of I. F. signal. I8 also designates generally a relay the contacts of which normally during operation are in the upper position but are moved to the lower position for tuning of the system. Y

22 designates generally the amplifier for increasing the carrier the desired amount, and this carrier as modulated is used to excite a conventional frequency multiplying transmitter.

24 is the power supply rectifier and transformer for the system. Y

It is believed that our improved control transmitter system as described briefly above will be readily understood by those skilled in the art. f

However, in order that the various novel and useful features thereof will be clearly recognized,

Va detailed description of the various elements will be given.

The tone generator tube 30 (Fig. 1, sheet 1) has its anode coupled to its control electrode by way of a phase shifting network comprising series condensers 32 and groups 34, 36 and 38 of shunting resistors. This tone oscillator is of the phase shift or R. C. type. Tuning is accomplished by changing the shunt resistance in each of the three sections 34, 36 and 38 of the phase shift network by adjustment of a ganged three deck rotary switch indicated at 48. Each of the groups of resistances includes eight diiferent resistances, so that eight different audio frequencies are provided. To insure reasonable frequency stability a voltage regulator tube 50 is connected across the high potential source supplying the screening electrode of tube 30. By this means the required stability is obtained without additional circuit compensation.

The generated tone is supplied by line 54 to an intensity adjusting potentiometer 56 and then to a resistance network 58, points of which are connected by a switch 60 to the input electrode of a tube 62 operating as a cathode follower amplifier.

The tone voltage necessary to produce a specie sweep of the I. F. oscillator in I6 varies with changes in the frequency of operation of the oscillator. We change the intensity of the tone voltage fed from 'I4 to the input of the reactance tubes in I6 by means of the resistances 58 cooperating with one deck 6G of the I. F. selector switch.

The drop across the resistor 63 is supplied to the telephone dial I0 and through the dialing mechanism to the primary winding of a transformer '14. The dialing mechanism Iii is manually controlled and pulses the audio frequency at a repetition rate of approximately 10 pulses per second. This permits the transmission of from 1 to l0 pulses per dial operation, since the dial has ten positions.

The output of transformer 14, as controlled by the dial l0, is fed differentially to the control electrodes 8| and 83 of the push-pull reactance tubes 88 and 82 which as connected control the timing of the oscillatory energy generated in tube 84. The tube 84 has its anode 86 and grid 38 coupled in a Hartley oscillator of the grounded grid type. This oscillator is tuned by a selected one of ve capacities C put in shunt to inductance L bythe second section of the I. F. selector switch. The capacities C are shunted by loading resistances to maintain constant output over the tuning range. Frequency stability over the range is provided by using zero drift condensers C and two series voltage regulator tubes 85 and 8l in the direct current supply to the anodes of tubes 36, 82 and 8d, and the screening electrodes of tubes 8B and 82. No other circuit compensation is needed. There are five capacities adapted to be switched into the circuitLC so that the intermediate 'frequency oscillator may operate at any one of live frequencies, depending upon the position of the section 96 of the I. F. selector switch.

The anode S6 of the oscillator 85 and one end of L are coupled to the anodes of the tubes 88 and 82 so that generated voltages of like phase appear on these anodes. The other end of the inductance L is connected through the cathode resistor 92 of tubes 88 and 82 and coupling condenser 94 to ground and thence to the lower terminal of the condenser' C. The grid electrode 38a ist. collpledr.. to; ground.; af biaSf lleslen; shuntedibyjcouplin ondens Ifo. we; considere th tank; clrcuitf. L.; resistance; 9&1(thefbiaseuesistance t5` shunted condenser 94: may;be ,d,i$11egard ed groundp and:V Q, we will; see .that;,-if;we assmefthe/-potential at the upper. endioflh andthefancdesfoitubes et; a1ld-82fis ot-a.Y rstr` phase, the phase of thefootentials Off thes generated frequency atk one: end,k of the-resistance: 92,3Wi11 be advanced'QO? withrespect .tosaid firstL phase, while theephase :of: thee generatedgvoltage; at'. the; other end ofthel resistance 92L will be refe 1ttrdedff,90withrespect to;said first phase.

More `exactly, we haveafnetwork, as, illustratedt in Figi I n thisnetworkggboth ends ,ofthebiafa res tance gaand condensen `lili max/be considered; ata.eroiirifl. radio frequency; potential This. iey permissible because 9,41; is large, enough to becomi-l` Sdelet-ashort circuit-at the generated-frequency?. (Infone embodimentd is 25 mfd.,and`bias; refe. sistince-,S is-390 ohms). The generated voltage, otEsaidy first phase-at point X is appliedto,the` anodes of both tubes B -andZ; The alternating; currentpath for `tube 3,2 may be considered from point; X through inductance --L, the resistance: 92;, (inone` embodiment 22j ohms), the cathode-.of tubef8.;2, andgbacl; to,-X.;V The current through` this network is rieactive, so that o there isl apoten?. talydrop through 92swhich is #displaced about` 9 0? at-thepathode of82r. This voltage isA also applied;` tn thegrid 8 1, oftube 8 9, rIvhe alternatingy cur-i rentgpath f or tube SELmay be considered from. the point X1throughfcondens er-V C, the. resistance, &2,the cathode-ofytube 8 8, andv back topoint,X This current is also reactive, butthe reactance is of opposite sign, so that the potentialzdrop, caused thereby in 92 is displaced in phase about 9 0? in theother direction at the cathodefofftube 8.1L This voltage'is alsogapplied:to-theJgrid S3,... oftube 82.` Thus We have `vinboth tubesit, and. 82a phase-quadrature relation between the anode1 and grid voltages. In one tube-the grid voltage leads, the, anode voltageYso that thev currentin., the-tube to thefanodeeleaols the anodevoltage andthe tube is in effect a capacity. in the taril;V A circuit:V In the other tube thel grid voltagelags.

the ,anode-voltage so that the current.in. thetube. lagsthe anode voltage-and the tube is. ineffect.A an inductance in the tank circuit. TheA positions ofthe inductanceL-andf condenser Cy may..v be,

interchangedg thus intercljiangingv the effective-1 reactances presented to theltrespectiye tubes in. the .tank circuit.

Differential modulation. rof the.; tubes. bypotene.. tials from the transformer 'ift thenwill, reduce the capacitive reactance and, theinductive reactance s'imultaneousy and vice versatoschangethe` frequency. 0f thev intermediate frequency. oscilla-v tions generated.

Thetiming modulated intermediate frequency; energy is .fed from L to a low impedance induct ance'Ll `and thence by` lines ,TL to a balanced,` potentiometer voltage dividerBP. Points on this; potentiometer orvoltage divider arel associated'. with two sections of the three section R.. F. 'ser lector switch Iilto apply the. timing modulated., intermediate frequency energy, in, a balanced sense-f and of proper amplitude A'for constant'. dea. viation lat the five-*different radio frequencies, to, the controlling electrcdesdl and.` l-il, of yreact-r ance tube modulatorslfand l It.y Ihescmodulaters are associated withy a radiofreouency oscillation generator includingtube I-ILhaVing. an

inductance L3V in a. grid circuit including the a ncetubes`l maandA Il0. The anode yof the tuberv H 2; is,` regeneratively; coupledv` byan inductancek Mutothednductance L3 so thatfoscillations are4 developed-in a wellknown manner. The highl potentialend of inductance L3 is coupled to they anodespf, tubesA |018- and H0, while the control; gridslfi.. and left are coupled to opposite terminals-rof, the resistancel H4 in a phase shifting network; quite fully described hereinbelore in con-. nectiongwith thegtubes 8 0 and Stand inductancc Liandresistance 9,2;A

The: frequency Of ythevcarrier energy gener-ated in tube H2; is-controlled by a third section of switch |00 cooperating with five condensersCS, theselectedonef of,l which is connected in shuntl tOi-thegrid circuitof tube H2 including inductanceT-fcmd resistor-H4. Note that the sections ofthe/,switch L06, are ganged rand that a differentv` intensity; of timing modulated oscillatory energyv of intermediate frequency is supplied to the inputv eleotrodesfl andlitof tubes |08 and lli) for each, particular frequency generatedin the radio frequency. generatormairita'inl the. frequency swing vthe saine at the various operating frequencies.

dueftoageinginthe modulator tubes is inherently compensated in the pushpull circuit. This is true alsofjthe. E'. generator and tubes 8i] and 82.

'Ifhegtubelz is ayradio frequency buffer ampleliof; thecathode follower type having its controlgrid coupled to the high radio frequency potential Aend of` inductance L31l and its cathode resistance coupledtothe control grid of tube |30. The tubefgi30` isthe ,output amplier tube and has itsyanode connectedgwiththe tank circuit including tuning condensercyand inductance L5.

Ther System..may be used: as the exciter of a transmitter; inr rwhich caseinductance L5 is coupled by inductance Leto transmitting apparatus.- This exciter supplies suicient voltage output fromv the low impedance-tank circuit C5, L5, Rlto drive-thefbuffer; tube of the'transrnitter for whichitfis intended In the present application thectankghe, is arranged to tune through a 5to 10:;megacycle rangeand the coupling through Lto `the-transmit/ter is arranged so that little or norfreactanceisreflected from the driven transmitterrftonthe exciter.- In some standard transmitters the tunedgstaees may; need damping in orderthatthey not attenuate the F. M. sidebands.

'24,' asnstated aboveisa conventional power sourceehavingfilament heating windings-and a rectifierarra-ngement which supplies potential to theftubes andzrelays.shown.

Before proceeding with the description and :operation of our transmitter, we will set forth briefly the nature of the receiver to be usedy therewith and the requirementsY of the transmitter as v4to wave form and modulation, etc., for oper ationof the receiver and relays in the manner desired.

In an embodiment of the receiver a novel, detecting system as well as a .novel relayy setup isV used'.

In the detecting`v system-double demodulationv takes -place'and in the intermedi-ate. frequency demodulator the detectorA output doubles the tone frequency supplied by the unit Ill. In other. words, where the oscillator I@ isfadaptedto A.operate `ata selected one of eight frequenciesrunning. resistance, [i4-,between theffcathodesof the react-V 7 5; from` 20.0 tot, 1290. cycles, Yatthe detector outputj The object of this is tol 7 one may select one of eight frequencies` running from 400 to 2400 cycles. This detected output includes in addition to the selected tone frequency a direct current component which is derived from the received and rectified carrier. The selected tone frequency is used to step up one of a series of dialing sensitive digital relays, there being four in the embodiment described, but there may be more if a larger number of combinations are desired. Absence of the direct current component derived by demodulation of the carrier is used to transfer operation of the tone frequency from one dialing sensitive digital relay to the next.

The direct current component depends upon the carrier and since in the operation at the receiver it is desired to interrupt the direct current component to thereby operate -a relay, we provide means at the transmitter for interrupting the carrier after each dialing operation. As stated above, the audio frequency is pulsed by the dialing system E at a repetition rate of about ten pulses per second, this permitting the transmission of l to 10 audio pulses per dial operation. At the completion of each dialed number the radio frequency is interrupted approximately for le second, this interruption being used to operate the transfer switch mentioned above, which conditions a second digital ratchet relay for operation, assuming that the first one was operated by the dialing described above.

In order to interrupt the transmitted carrier to initiate this transfer function at the receiving terminal equipment, the relay |30 is so connected that it is energized for about 11-0 of a second, after each dialing operation, by closure to the right of the dialing mechanism contacts |35. Closing these contacts puts the condenser |36, which has been charged during the dialing operation (contact |35 closed at left and remaining closed by an off-normal contact until the dial has returned to its normal quiescent position), in series with the winding i3? to energize the same to close a contact |39 which includes the condenser |40 across the radio frequency oscillation generator tank L3, C3. This condenser detunes the tank oscillator and the exciter for the transmitter t0 such an extent that as far as the receiver is concerned the signal is removed. Where this exciter unit is used with a transmitter, we contemplate use of this relay in a keyable circuit in the tr-ansmitter, since its function is to interrupt the transmission after each number dialed.

In operation, the power supply A. C. switch |10 should be turned on three minutes before operating the unit, to allow for frequency stabilization. If this switch is turned off, it must not be turned on until the heaters have cooled about one minute, to allow the initial power supply B voltage to reach -a value that will ignite the gas regulator tubes.

The I. F. relay switch |80 should be set to the "Tune position, that is, closed to the right hand contacts. This places the Winding of relay |84 across the power supply and the relay is pulled down to connect the grids of reactance tubes |08 and H0 to ground, the input from stage I6 being thereby removed. The R. F. selector switch |00 is set to the desired frequency and the output amplifier tuning dial on condenser C5 is set to the point previously found as tuning to the corresponding frequency.

Remembering that the exciter output at L5 is one quarter of the frequency at the final output after multiplication in the transmitter, the transmitter is tuned in the usual mannerY to quadruple the exciter frequency. In an embodiment the exciter frequency is in a band from 5 to 8 megacycles and the transmitter output in a band of 20 to 32 megacycles. The transmitter is then switched to the Standby position and the I. F. relay switch on the exciter unit is switched to Operate, that is, closed to the left. This deenergizes the winding of relay |84, and the grids of the reactance tubes |08 and l0 are connected to the balanced resistance network BP to be excited by the tone modulated output of the stage I6. The equipment is now ready to operate. Moreover, since the digital relays and other relays in each of the various receivers are frequency sensitive and respond to one particular tone frequency only and the various receivers also select only a particular intermediate frequency, operation on any of the 400,000 combinations possibler on one radio frequency can be carried out. There are five different carrier frequencies from which to select, thereby giving a total of 2,000,000 posslble combinations. i

When a certain receiver is to be dialed, the A. F. and I. F. tuning dials are set and the transmitter is switched from Standby to Operate The proper number is dialed and the transmitter is returned to Standby In order to allow other receiving equipment to home, that is, permit their relays to return to their original settings, a period of five seconds should elapse before dialing another receiver having the same R.F. and I. F. When one receiver is used to operate two or more detonators on different dialed numbers, this homing sequence must be carefully observed.

We claim:

1. In a signalling system of the class described, a first source of potentials of tone frequency, a second source of wave energy of carrier wave frequency the frequency of which may be adjusted by steps through a range of frequencies, a modulator associated with said second source for modulating the said wave energy of carrier wave frequency, an attenuatng network comprising adjustable voltage attenuating impedances coupled to said first source and to said modulator, a dialing circuit in one of said couplings for pulsing the tone applied to said modulator through a range of pulses and common control means for adjusting the impedance of said attenuating network and the frequency of said second source to insure modulation of the selected carrier through a predetermined range by the tone frequency potentials.

2. In a signalling system of the class described, a rst source of potentials of tone frequency, a second source of wave energy of carrier wave frequency the frequency of which may be adjusted by steps through a range of frequencies, a modulator associated with said second source for modulating the timing of said wave energy of carrier wave frequency, an attenuating network comprising adjustable voltage attenuating impedances coupled to said first source and to said modulator, a dialing circuit in one of said couplings for pulsing the tone applied to said modulator through a range of pulses and common control means for adjusting the impedance of said attenuating network and the frequency of said second source to insure timing modulation of the selected carrier through a predetermined range by the tone frequency potentials.

3. In a signalling system of the class described,

a source of control potentials, a rst source of' gewogen AWave y `energy fof .'fcarrierwave'frequency ath'ecfrequencyfof whichimayzbe adjustedbysteps through -a range :of ffrequencies,faarmodulator associated with-said first Vsourced wave enemvySforf-modulatf ing? the 'said 'wave 'e'neigy'ofioarri Swayefrequency, i an *attenuating network corrilprisingad'j ustable voltage vattenuating Ilmpedances coupling said source fof control i potentials to said i modulator, "common control-meansfor-adjusting-theimpedance of said attenuating netwrkiand thefrequency of said first source toinsure modulation of the selected-'carrierthr0ugh*$pr`determined range by the control:potentialsfarsecond source of oscillan tions of carrier.wavefrequency,. and a modulator connected to sadr's'tcarrier source and to said Irlsecondfrcarrierlsource for; modulatingthe oscillations of said second source of 'oscillations e'f carrier wave yfrequencyiniacccrdance :with modulated carrier energy from said first wave energy i4. c:on asignan-ing' systemr or theiciasszdescnbed,

network comprising adjustable voltage attenuating impedances coupling said source of control potentials to said modulator, common control means for adjusting the impedance of said attenuating network and the frequency of said rst source of carrier wave frequency to insure timing modulation of the selected carrier through a predetermined range by the control potentials, a second source of oscillations of carrier wave frequency, and a reactance tube modulator coupled to said first and second sources of carrier wave frequency for modulating the timing of the oscillations of said second source of oscillations of carrier wave frequency in accordance with the first mentioned timing modulated wave energy.

5. In a signalling system of the class described, a first source of oscillations of tone frequency, a second source of wave energy of carrier Wave frequency, a modulator associated with said sec ond source and said rst source for modulating the said wave energy of carrier wave frequency in accordance with said tone frequency, a dialing crcuit having an input coupled to said first source and an output coupled to said modulator for pulsing the tone supplied to said modulator through a range of pulses, transmitting means coupled to said second source, and means for suppressing transmission following each operation of said dialing circuit.

6. In a signalling system of the class described, a rst source of oscillations of tone frequency, a second source of wave energy of carrier wave frequency, a modulator associated with said sec ond source and said first source for modulating the timing of said wave energy of carrier wave frequency in accordance with said tone frequency, a dialing circuit having an input coupled to said first source and an output coupled to said modulator for pulsing the tone supplied to said modulator through a range of pulses, a third source `of wave energy of carrier wave frequency, conm nections from said second source to said third source for modulating the timing of the osciliations of said third source in accordance with the timing modulated oscillations from said second source, transmitting means coupled to said third source of wave energy of carrier wave frequency,

and means for suppressing `transmission thereifrom vfollowing each operati-on lofsaid dialing rcircuit.

'7. In=` a' signalling system ofthe-class described, VVfa rst source of Aiwave-energy the frequencyvof rwhl ch @may Vbe* raltered bygsteps throughy a frange vof frequencies, `la secondrsource of wavefenergy ofcarrier-:fwave frequencyfthe frequency'ofcwhi'ch i may.` be adjusted, connections for :modulatingr selectedcarrieri frequency from said secondsource sthroughv a z predetermined :range 1 by 1 waveenergy Stof :fa selected frequency .from said i rst source, transmittingmeans-coupled to said.v second source, means ingsafidrrstifnamed. connections forbreak- .ingfiup the .fwave v"energy of :selected frequency, `usedrtoimodulate :said secondizsource, to formzia :ciselected'numberzof =pulses, zand means for :sup-

pressing transmission from fsaid vsecond .source i intermittently between pulsesor groups of. pulses. t 8. In arsignalling system Lof the class described, .elaftfirst source kcof; oscillations kof tone frequency i theffrequency :of whichf'may be altered 'byxrsteps througha ran'gezoffrequencies, a secondrsource of 'awav'e -energy `of l:carrier fwave frequencyxthe vfrequency of `which inay 'befadjustedconnections forirmo'dulatinga-v selected carrier frequency-from 4said "second vsource v:through 1a z'predetermined range'fby "a selected? tone v:from saidrgrrstrsourca *means inesaid! first. named :connectionsrfon breaking up the selected tone, used to modulate said second source, to form a selected number of y pulses, a third source of oscillations of carrier wave frequency, means for modulating said last named source in accordance with the modulated output of said second source, transmitting means coupled to said last named source, and means for suppressing transmission therefrom between pulses or groups of pulses.

9. In a signalling system of the class described, a first source of oscillations the frequency of which may be altered by steps through a range of frequencies, an amplifier having an input and an output, a second source of wave energy of carrier wave frequency the frequency of which may b e adjusted by steps through a range of frequencies, an attenuating network comprising adjustable Voltage attenuating impedances, couplinff said first source to said amplifier input, a. modulator associated with said second source for modulating the said wave energy of carrier wave frequency, a dialing circuit coupling said amplifier output to said modulator and common control means for adjusting the impedance of said attenuating network and the frequency of said second source to insure modulation of the selected carrier through a predetermined range by the first oscillations.

lO. In a signalling system, a source of wave energy of tone frequency. a source of wave energy of intermediate frequency, a source of wave energy of carrier frequency, means for modulating the timing of the wave energy of intermediate frequency in accordance with the energy of tone frequency, means for modulating the timing of the energy of carrier Wave frequency in accordance with the timing modulated intermediate frequency energy, means for changing the frequency of said second and third mentioned sources by predetermined amounts, means for changing the amplitude of the tone energy when the frequency of the second mentioned source is changed, and means for changing the amplitude of the timing modulated intermediate frequency energy when the frequency of the third mentioned source is changed.

11. In a signalling system, a source of oscil latory energy of tone frequency the frequency of which may be changed by steps through a range of frequencies, a source of oscillatory energy of intermediate frequency and a pair of modulator tubes associated therewith, a controllable pulsing system coupling said source of oscllatory energy of tone frequency to the pair of modulator tubes, means for selectively changing the frequency of the intermediate frequency oscillations by steps through a range, a carrier wave generator the frequency of operation of which may be changed by steps in a range of frequencies, a second pair of reactance tube modulators associated with said carrier wave generator, and a coupling between said intermediate frequency oscillatory source and said last mentioned pair of reactance tubes.

12. In a signalling system, a source of oscillatory energy of relatively low frequency, the frequency of which may be changed through a range of frequencies, a source of oscillatory energy of intermediate frequency, a modulator tube coupled to said last named source, a controllable pulsing system coupling said source of oscillatory energy of relatively low frequency to said modulator tube, apparatus for selectively changing the frequency of the intermediate frequency oscillations through a range of frequencies, a wave generator of carrier wave frequency, the frequency of operation of which may be changed through a range of frequencies, a second modulator tube coupled to said last named generator of carrier wave frequency, and apparatus coupling said source of intermediate frequency to said last named modulator tube for modulating the oscillations of carrier wave frequency in accordance with the modulated oscillations of intermediate frequency.

JOHN A. RANKIN.

WILLIAM R. ALEXANDER.

HARMON B. DEAL.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,036,165 Usselman Mar. 31, 1936 2,131,558 Granger Sept. 27, 1938 2,162,335 Jacob June 13, 1939 2,233,183 Roder Feb. 25, 1941 2,274,648 Bach Mar. 3, 1942 2,309,678 Smith Feb. 2, 1943 2,339,608 Alvira Jan. 18, 1944 2,355,338 Stewart Aug. 8, 1944 

